1. Field of the Invention
This invention is related to boots whose bottom assembly is made according to a stratified structure having several layers, each fulfilling a separate function. More specifically, this invention is related to the coupling of a reinforcement element of the upper with one of the layers of the bottom assembly.
2. Description of Background and Relevant Information
Boots of the aforementioned type have been described in U.S. Pat. No. 5,317,820 and published European Application No. 0 748 596. More specifically, in the example of U.S. Pat. No. 5,317,820, the reinforcement element of the boot upper is coupled to a bottom assembly that includes, from the base upwards:
a wearable layer, made of rubber, that comes in contact with the ground; PA1 an intermediate layer, made of rubber, having a lateral edge that extends rearwardly in order to retain the user's heel; and PA1 another semi-stiff upper layer, made of a plastic material, that extends in correspondence with the plantar surface of the user's foot. PA1 making the reinforcement of the upper and the bottom assembly interdependent so as to improve the stability of the foot in view of proper movement thereof, the precision of the supports in the bottom assembly/ground interface, and the grip of the wearable layer of the bottom assembly on the ground by making it more incisive; PA1 dampening the shocks during the impact of the bottom assembly with the ground without altering the foot stability; PA1 guaranteeing an optimum comfort level in the foot/bottom assembly interface without cutting off the necessary perception of the bottom assembly supports on the ground; PA1 restoring a portion of the energy used during shock absorption so as to stimulate rebound during the movement of the foot, at least during the propulsion phase. PA1 an efficient coupling of the reinforcement element and the core layer of the bottom assembly with the wearable layer in contact with the ground because the reinforcement of the upper is made interdependent of the bottom assembly without there being any interference with an intermediate shock absorbing layer; PA1 an extremely good shock absorption in the bottom assembly/ground interface because the spacing of the reinforcement element with respect to the heel of the bottom assembly leaves the heel free to bend during impacts with the ground, which furthermore respects satisfactory foot movement during the shock absorption phase; PA1 a good absorption of shocks because such shocks are dispersed, and thus dampened, firstly, at the level of the wearable layer; secondly, in the area of the core layer, which, due to its stiffness in torsion and bending, disperses them even further over almost its entire surface; and thirdly, in the area of the comfort layer, which dampens their residual intensity even further, before they reach the foot; PA1 an optimum level of comfort in the bottom assembly/foot interface because the plantar surface of the foot rests directly on an elastic shock absorbing layer that ensures a flexible contact especially in the area of the foot supports; PA1 a certain capacity to stimulate rebounding during the movement of the foot because, on the one hand, the elastic shock absorbing layer, by its very nature, pushes the foot back in order to readopt its initial shape in the manner of an elastic return during the movement of the foot during the propulsion phase, and, on the other hand, due to the bending freedom of the heel of the bottom assembly with respect to the reinforcement of the upper, the elastic return into the initial position of the latter leads to the same rebound effect.
According to the construction disclosed and taught, it is from this latter upper layer, made of a plastic material, that the reinforcement element originates, the element being constituted of two lateral supports rising up the sides of the upper of the boot.
By virtue of this structure, the semi-stiff upper layer, which constitutes the core of the sole, can be biased so as to vary in position with respect to the ground depending on the forces applied on the upper by means of the lateral supports that form the reinforcement element thereof. As a result, this reinforcement element supports the forces borne by the upper, especially during use, and transmits them directly to the bottom assembly of the boot via the semi-stiff upper layer from which it originates, and vice versa.
In fact, by obtaining the coupling of the reinforcement element with the semi-stiff upper layer, the upper and the bottom assembly become interdependent, thereby improving the lateral retention of the user's foot in the boot, and thus the stability of the shod foot. However, the efficiency of this coupling has proven to be random, or at least inadequate when it comes to achieving good adherence and efficient gripping, since the stiffness obtained in the area of the wearable layer which comes in contact with the ground, or at the bottom assembly-ground interface level, depends not only on the mechanical properties of the semi-stiff upper layer with its reinforcement, but also depends on the mechanical properties of the intermediate rubber layer that is inserted between it and the wearable layer. As regards the intermediate rubber layer, which is inherently shock absorbing, and also adds material thickness to the bottom assembly on the side that is furthest from the plantar surface of the user's foot, there is a substantial dispersion of shocks and stresses in this area, and elastic deformations also occur, which have a detrimental effect on the expected lateral retention of the foot, by means of the reinforcement element, and therefore on the stability during the impact of the bottom assembly with the ground. The precision of the supports of the bottom assembly on the ground are also changed.
In addition, another disadvantage lies in the fact that the semi-stiff upper layer is located immediately across from the plantar surface of the user's foot.
Indeed, in such a situation where the foot takes direct support on a relatively hard surface, the repeated compressions that the latter is subject to at the point of such supports when the boot is used often causes painful sensations, even minute traumas, that are manifested, for example, by chafing, blisters, cramps, etc.
In the example of European Application No. 0 748 596, the boot disclosed therein differs from the previously described boot mainly in the fact that the bottom assembly does not have a shock absorbing upper layer, or comfort layer, between the semi-stiff upper layer provided with the reinforcement element and the wearable layer that comes in contact with the ground. Indeed, the boot includes, on the one hand, a bottom assembly that is obtained according to a stratified structure having several layers respectively fulfilling distinct functions, or at least one wearable layer and one core layer, and, on the other hand, one reinforcement layer for its upper that is coupled to that of the layers of the bottom assembly that constitutes its core layer, the latter being directly arranged on the wearable layer that comes in contact with the ground. The overall structure which results from such an arrangement provides greater efficiency to the coupling of the reinforcement element with the upper layer, which are preferably made from an injected plastic material, and therefore equipped with a certain stiffness.
Indeed, according to this construction, there is no dispersion of shocks and stresses between the wearable layer that comes in contact with the ground and the upper layer that constitutes the core of the sole and is provided with the reinforcement element. Consequently, all the biases and stresses that occur between the reinforcement element and the intermediate layer from which the latter originates are directly transmitted to the wearable layer that comes in contact with the ground and vice versa. As such, there is optimal synergy between the reinforcement element of the upper and the bottom assembly which allows for a substantial improvement in the overall behavior of the boot in dynamic gripping and adherence onto the ground, as well as in precision and stability, especially by virtue of the stiffness in torsion and bending achieved in the bottom assembly/ground interface obtained in this manner.
However, such a bottom assembly, i.e., with no intermediate shock absorbing layer or comfort layer, has proven to be especially ill-suited in ensuring a transfer function capable of correctly dampening shocks in the area of the user's foot at each contact with the ground, i.e., there is no shock absorption. Such a transfer function with shock absorption is essential in the bottom assembly for a good foot movement, which generally occurs in three phases, absorption-support-propulsion, and prevents certain types of traumas that almost always occur due to the intensity of the shocks and their frequency in the sensitive zones of the plantar surface of the foot, such as, for example, the heel zone where overloads are substantial.
Indeed, in some sports, such as hiking, especially when walking down a slope, or in sports such as running, the heel of the boot hits the ground rather violently at the moment of impact and the reactional forces from the ground can reach values that are equal to several times the user's body weight.
Therefore, it is easy to understand that the absorption function of the bottom assembly is especially important during this first phase of the foot movement, so as to absorb at least part of the shock energy that is produced at that moment and disperse it through elastic deformation, and thus avoid overloads that generate injuries.
In addition, as was the case with the bottom assembly described previously with reference to U.S. Pat. No. 5,317,820, the upper layer that constitutes the core of the sole is immediately across from the plantar surface. Consequently, the same problems of discomfort are also found in the foot/sole interface.